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Carbohydrate feeding during exercise.

E F Coyle1

  • 1Dept. of Kinesiology and Health, University of Texas, Austin.

International Journal of Sports Medicine
|October 1, 1992
PubMed
Summary
This summary is machine-generated.

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Consuming carbohydrates during strenuous exercise delays fatigue by 30-60 minutes. This requires significant exogenous glucose to maintain blood glucose levels and fuel prolonged endurance exercise.

Area of Science:

  • Exercise Physiology
  • Sports Nutrition
  • Metabolic Research

Background:

  • During strenuous exercise (70% maximal O2 consumption), the body shifts from using muscle glycogen to blood glucose for energy.
  • Maintaining adequate blood glucose is crucial for sustaining high-intensity exercise duration.

Purpose of the Study:

  • To investigate the role of exogenous glucose in sustaining prolonged strenuous exercise.
  • To determine the required rates of glucose supplementation to maintain blood glucose levels and carbohydrate oxidation during endurance exercise.

Main Methods:

  • Subjects performed strenuous exercise at 70% maximal O2 consumption for extended durations.
  • Intravenous glucose infusions were used to maintain specific blood glucose concentrations (5 mM and 10 mM).
  • Carbohydrate oxidation rates and muscle glycogen utilization were assessed.

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Main Results:

  • Exogenous glucose supplementation delays fatigue by 30-60 minutes in endurance-trained individuals.
  • Rates exceeding 1 gram/min (16 mg/kg/min) of glucose infusion are needed to maintain blood glucose at 5 mM.
  • To maintain blood glucose at 10 mM after 2 hours, infusion rates of 2.6 grams/min (37 mg/kg/min) are required.
  • Carbohydrate supplementation does not spare muscle glycogen utilization during intense exercise.
  • Muscle glycogen and blood glucose contribute equally to carbohydrate oxidation during 2-4 hours of exercise at 70% VO2max.
  • Exogenous glucose can supply nearly all carbohydrate needs at this intensity in later stages of exercise.

Conclusions:

  • Maintaining blood glucose through exogenous supplementation is critical for delaying fatigue during prolonged strenuous exercise.
  • High rates of glucose infusion are necessary to sustain elevated blood glucose levels during endurance exercise.
  • While not sparing muscle glycogen, blood glucose becomes a primary fuel source during prolonged exercise, with exogenous sources capable of meeting these demands.